U.S. patent number 6,366,815 [Application Number 09/331,838] was granted by the patent office on 2002-04-02 for implantable nerve stimulator electrode.
This patent grant is currently assigned to Neurodan A /S. Invention is credited to Hans Harding, Morten Haugland.
United States Patent |
6,366,815 |
Haugland , et al. |
April 2, 2002 |
Implantable nerve stimulator electrode
Abstract
The invention relates to an implantable stimulator electrode for
stimulation of nerves adapted to be surgically implanted around a
nerve bundle, said stimulator comprising one or more electrode
means which, when implanted around said nerve bundle, surrounds the
nerve bundle totally or partly. Electrode means and electronic
circuit means are coupled to and powered by one or more receiving
coils mounted on the stimulator housing. One advantage of the
invention is that the electrode, when implanted, acts as a remote
addressable maintenance free unit.
Inventors: |
Haugland; Morten (Aalborg,
DK), Harding; Hans (Aalborg, DK) |
Assignee: |
Neurodan A /S (Aalborg,
DK)
|
Family
ID: |
8089099 |
Appl.
No.: |
09/331,838 |
Filed: |
August 18, 1999 |
PCT
Filed: |
January 13, 1998 |
PCT No.: |
PCT/DK98/00010 |
371
Date: |
August 18, 1999 |
102(e)
Date: |
August 18, 1999 |
PCT
Pub. No.: |
WO98/30279 |
PCT
Pub. Date: |
July 16, 1998 |
Foreign Application Priority Data
|
|
|
|
|
Jan 13, 1997 [DK] |
|
|
0044/97 |
|
Current U.S.
Class: |
607/48;
607/118 |
Current CPC
Class: |
A61N
1/0556 (20130101); A61N 1/36125 (20130101); A61N
1/37205 (20130101) |
Current International
Class: |
A61N
1/36 (20060101); A61N 1/05 (20060101); A61N
001/36 () |
Field of
Search: |
;607/118,40,30,32,41,45,46,61,48,49,36,116 ;128/903 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2 239 802 |
|
Jul 1991 |
|
GB |
|
92/15366 |
|
Sep 1992 |
|
WO |
|
Primary Examiner: Schaetzle; Kennedy
Attorney, Agent or Firm: Dykema Gossett PLLC
Claims
What is claimed is:
1. An implantable stimulator for stimulation of nerves and adapted
to be surgically implanted around a nerve bundle, said stimulator
comprising:
a housing in the form of a cuff, electrode means which, when
implanted at least partially surrounds said nerve bundle,
electronic circuit means having output terminals coupled to said
electrode means, including input terminals for receiving an input
signal, at least one receiving coil mounted on the housing, and
wherein the input terminals are coupled to the at least one
receiving coil.
2. An implantable stimulator according to claim 1, wherein the
electrode means, when implanted around said nerve bundle, comprises
at least one electrode at least partly surrounding the nerve bundle
defining a contact area, each contact area being electrically
coupled to the output terminals of the electronic circuit
means.
3. An implantable stimulator according to claim 2 wherein the
electrode means comprises three ring-shaped electrodes.
4. An implantable stimulator according to claim 1 wherein the
electrode means, when implanted around said nerve bundle, comprises
at least one ring-shaped electrode at least partly surrounding the
nerve bundle, each ring-shaped electrode comprising at least two
distinct electrode contact areas, each electrode area being
electrically coupled to the output terminals of the electronic
circuit means.
5. An implantable stimulator according to claim 1, wherein the
electrode means comprises at least two electrode contact areas, the
electronic circuit means comprises multi-channel pulse shaping
electronics means, each input terminal being coupled to a separate
receiving coil, each output terminal being coupled to a
corresponding electrode contact area, said channels of said pulse
shaping electronics means having a separate receiving
frequency.
6. An implantable stimulator according to claim 1 wherein at least
a portion of the stimulator is encapsulated within a biologically
inert substance.
7. A transmitter/stimulator system comprising at least one
transmitter and at least one implantable stimulator according to
claim 1, each transmitter comprising a control circuit, said
control circuit controlling and activating a transmitting stage,
said transmitting stage converting electric signals to
electromagnetic signals, wherein each transmitter comprises at
least one transmitting coil adapted to be positioned in space
relationship on each side of each of said at least one
stimulator.
8. An implantable stimulator for stimulation of nerves and adapted
to be surgically implanted around a nerve bundle, said stimulator
comprising:
a housing,
electrode means which, when implanted comprises at least one
ring-shaped electrode at least partially surrounding said nerve
bundle, electronic circuit means having output terminals coupled to
said electrode means, including input terminals for receiving an
input signal, at least one receiving coil mounted on the housing,
and wherein the input terminals are coupled to the at least one
receiving coil, said electrode further comprising at least two
distinct electrode contact areas, each electrode area being
electrically coupled to the output terminals of the electronic
circuit means.
9. An implantable stimulator for stimulation of nerves and adapted
to be surgically implanted around a nerve bundle, said stimulator
comprising:
a housing,
electrode means which, when implanted at least partially surrounds
said nerve bundle, electronic circuit means having output terminals
coupled to said electrode means, including input terminals for
receiving an input signal, at least one receiving coil mounted on
the housing, and wherein the input terminals are coupled to the at
least one receiving coil, and
wherein the electrode means further comprises at least two
electrode contact areas, and the electronic circuit means further
comprises multi-channel pulse shaping electronics means, each input
terminal being coupled to a separate receiving coil, each output
terminal being coupled to a corresponding electrode contact area,
said channels of said pulse shaping electronics means having a
separate receiving frequency.
Description
BACKGROUND OF THE INVENTION
The invention relates to an implantable electrode for stimulation
of nerves adapted to be surgically implanted around a nerve
bundle.
Restoring motor-functions of (partially) paralysed people is known
by exploiting the fact that muscles respond to electrical energy.
This principle can be utilised to directly stimulate muscles or to
stimulate the nerves leading to the muscles. Direct stimulation of
muscles requires a number of electrodes distributed on the muscle,
compare e.g. U.S. Pat. No. 5,314,458, and is relatively power
consuming. In addition, the control equipment is rather complicated
for surveillance of the electrodes to achieve the desired movement
of the muscle.
Stimulation of nerves can be made by placing electrodes locally
around the nerves which is known from e.g. U.S. Pat. No. 5,038,781.
For this reason the surgical intervention is minor. Stimulation of
nerves also requires much less energy than stimulation of muscles
although the power requirement is still high compared to e.g. a
pacemaker due to the higher stimulation frequency necessary to
obtain smooth contractions of muscles. The present invention
relates to nerve stimulation.
The controlling equipment and the power supply are placed
externally on the human body and could be connected to the
electrodes by using wires passing through the skin which for
obvious reasons is not an attractive solution. Alternatively, the
placement of a transmitter on the body and an implant of a receiver
in the body wired to the electrodes is also known, said transmitter
sending signals and energy through the skin and flesh to the
receiver. More specifically, the present invention relates to the
latter type of stimulator electrodes.
Such a neurological stimulation apparatus is known from e.g. U.S.
Pat. No. 5,038,781 said apparatus comprising nerve cuffs with
electrodes attached to a nerve bundle and wire connected to an
implant case containing the electronic circuitry receiving
operating power and information signals by radio frequency coupling
to an external unit. Running wires under the skin and implanting a
casing in the body is for obvious reasons not an attractive
solution.
Another example is known from U.S. Pat. No. 4,057,069 which deals
with an implantable nerve stimulator receiving energy from an
external unit by telemetrically transferring energy from an
external unit. The nerve stimulator contains a detector circuit
which by an adequate excitation can address a number of electrode
pairs of a multiplexer. The nerve stimulator has among other things
the disadvantage in connection with multielectrode systems of not
being able to address all of these simultaneously, however, only
sequentially. In addition, the nerve stimulator is limited locally,
as the electrode pairs in question necessarily have to be in
galvanic contact with the nerve stimulator itself.
A further example is known from U.S. Pat. No. 3,667,477 which deals
with an implantable nerve stimulator which receives energy from an
external unit by telemetric transmission. The implantation of the
disclosed nerve stimulator, however, is quite complicated, as the
stimulator is made of separate receiving and electrode means
coupled by leads.
It could be mentioned that it is also known to stimulate muscles by
means of telemetric transmission.
An example is known from U.S. Pat. No. 5,314,458 which deals with
an implantable muscle stimulator which receives energy from an
external unit by telemetric transmission. This unit can be
addressed individually, however, due to its placement on the muscle
itself a very powerful excitation is needed and subsequently a very
powerful electromagnetic field which causes the electromagnetic
transfer of energy to be less attractive considering the continuing
influence of the surrounding tissue. In addition, it is needed that
the stimulator is being widely controlled when stimulating a muscle
complex, as a certain number of specific controlled stimulators is
needed in order to obtain an appropriate movement of the
muscle.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an improved and
simplified neurological stimulation apparatus. A further object is
to minimise the surgical intervention when applying the apparatus
in the body.
When according to the present invention the input terminals coupled
to one or more receiving coils are mounted on the stimulator
housing, a remote individual addressable stimulator for stimulation
of nerve bundles is obtained thus being able to function as an
isolated implanted unit. When implanted, the stimulator will be
placed in a juxta position or around the nerve being stimulated.
According to the invention there is no need for any lead
connections between the stimulator and external circuits, in the
sense that the transmitter can be activated on location by remote
signals without any need for an internal power source.
The control of the stimulator or the stimulators and the resulting
activation of muscles is made even more simple due to the fact that
a stimulation of the nerve often is less complicated than a
stimulation directly on the muscles which are to be activated. In
the case when a group of muscles or a muscle with multiple motor
points innervated by the same nerve are wished to be activated at
the same time (as for example in the case of dropfoot stimulation),
it is advantageous to use one multichannel nerve stimulator placed
on the nerve compared to many individual stimulators placed in the
muscles.
According to the invention it is thus possible to obtain a remote
stimulation using a minimal electromagnetic field.
Coupling the input terminals to one or more receiving coils mounted
on the stimulator/electrode housing, it is possible to obtain a
necessary power supply to the electrodes and the electronic circuit
means which is provided telemetrically via the receiving coil or
receiving coils, thus avoiding the use of lead connections between
the internal part of the stimulator and the external part of the
stimulator. It is thus possible to avoid battery powered
electrodes.
Furthermore, the transmitter is basically free of maintenance in
the sense that replacement of implanted power sources or the like
is not needed.
In this connection, it is noted that the necessary effect needed to
stimulate the nerves is approximately ten times lower than the
necessary effect needed for direct stimulation of muscles. By
stimulating the nerves rather than the muscles, a remote activation
of the stimulator is particularly attractive.
The risk of complications due to the surgery activity required to
implant the stimulator is moreover reduced in the sense that the
stimulator itself, according to the invention, can be realised in a
very compact design in contrary to e.g. lead-connected systems.
The stimulator according to the invention is especially applicable
in situations where a continuing or periodically stimulation of the
muscle is needed, as the implanted stimulator under constant
influence of movement is mechanically as well as electronically
stable and sturdy in the sense that neither the electrical nor the
mechanical parts undergo stress during said movement which also
results in a minimised risk of IN VIVO complications.
In addition, the use of an external power source will in practise
result in a minimised risk of noise signals activating the
stimulator as these external noise signals necessarily have to
reach a certain noise level at a given wavelength in order to
activate the electrodes of the stimulator.
Accordingly, in a further embodiment of the invention, the
electrode means, when implanted around said nerve bundle, comprises
one or more circle-shaped or semi-circumferential electrodes
defining a contact area, each contact area being electrically
coupled to the output terminals of the electronic circuit means.
(Totally or partly surrounding the output terminals). This
particular "shape" of the electrode means thus makes it possible to
obtain a very well-defined positioning of the stimulator as regards
the nerve bundle and at the same time, the electrode means create
good contact between the electrode means and the nerve bundle.
When the electrode means, when implanted around said nerve bundle,
comprises one or more ring-shaped electrodes totally or partly
surrounding the nerve bundle, each ring-shaped electrode comprising
at least two distinct electrode contact areas, each electrode area
being electrically coupled to the output terminals of the
electronic circuit means, it is possible to obtain a stimulator
which is able to make a selective stimulation of the nerve and the
associated muscles. The stimulation of the nerves can be obtained
in various ways depending on which result is wanted. The
stimulation can thus be obtained by a mono- or multipolar
electrical stimulation, the chosen multipolar electrode stimulation
being transverse, e.g. effected by electrodes on the same ring
electrode or longitudinal, e.g. effected by electrodes on different
rings. Furthermore, it is possible to combine transverse and
longitudinal stimulation. The stimulator thus has the possibility
of being used with an overall degree of selectivity which can be
chosen from known mono- or multipolar configurations.
In a multichannel stimulator, each channel has its own electronic
circuit connected to a separate receiver coil. The only difference
between each channel is the resonance frequency of which each
channel is active. The main purpose of the electronic circuit is to
create an adequate stimulation pulse shape.
When each transmitter comprises one or more transmitting coils
positioned in spaced relationships on each side of one or more of
the stimulators, it is possible to obtain a very useful remote
activated stimulator system.
BRIEF DESCRIPTION OF THE DRAWINGS
Below, the invention will be further explained with reference to
the accompanying drawing, wherein
FIG. 1 shows a stimulator according to the invention,
FIG. 2 illustrates, by means of an electrical schematic diagram, a
preferred embodiment of the receiver portion of the stimulator.
FIG. 3 illustrates a two channel stimulator according to the
invention,
FIG. 4 shows a schematic drawing of a limb with stimulator and
transmitter coils.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIG. 1 there is shown a stimulator according to the
invention, said stimulator comprising a receiver coil 3 which is
coupled to an electrical circuit 2. The electrical circuit 3 is
furthermore connected to electrodes 6 and 7.
The electrode 6 is a feeding electrode coupled to one output
terminal of the electrical circuit 3, while the electrodes 7 are
return electrodes, coupled to the common output terminal of the
electrical circuit.
The stimulator is encapsulated in a cuff made of a biologically
inert substance 4 such as silicone rubber or the like. For
placement of the cuff around a nerve, the cuff is slit length-wise
in a zip-like manner.
The invention provides a very compact design of the stimulator by
incorporating the receiving coil in the stimulator housing or
stimulator body, and it is thus possible to implant the stimulator
properly without the use of lead connection between co-operating
stimulators or an external power supply.
Referring now to FIG. 2, there is shown a preferred embodiment of
the receiver portion of the stimulator.
The receiver portion of this embodiment includes a receiver coil 10
in parallel with a capacitor 18 at junctions 32 and 31. The
component values of the coil 10 and capacitor 18 are such that the
circuit resonates at a selected receiver frequency.
A rectifier diode 11 is coupled to a filter capacitor 19 at a
junction 33, which capacitor 19 is further connected to the common
junction 32. The diode 11 rectifies an incoming signal and the
filter capacitor 19 acts as a filter or bandpass filter for
smoothing the signal and removing thigh frequency components of the
rectified signal. Furthermore, a zenerdiode 22 is coupled in
parallel with the capacitor 19.
A JFET transistor 11 is coupled between the junction 33 and
junctions 34, 35, the latter being connected to the gate of the
JFET 11. The JFET transistor 11 limits the current to between 1 to
2 mA which is a sufficient stimulation current.
A resistor 20 is coupled between the junctions 35 and 32. A diode
14 is followed by a capacitor 15 connects an electrode 16 to the
junction 35, and a transistor 21 is coupled to the junctions 35, 36
and 32.
The common junction 32 is furthermore coupled to two electrodes
17.
The circuit following the current limiting transistor 12 has the
primary function of balancing the charge fed to the electrodes/put
out on the electrodes, as the stimulation of a nerve bundle will
have to be without any DC-components ensuring that the nerves are
not damaged by the injected charge. The balancing circuit, thus
secures that the charge lead into the stimulated nerve equals the
charge taken out from the nerve.
The stimulation current is controlled by a current limiter
consisting of the J-FET T2. As there is a great manufacturing
spread in the drain current of these, the units which when measured
are found to have a drain current between 1 and 2 mA are chosen.
This circuit is principally sufficient when stimulating a nerve,
however, since the nerve can be destroyed if only one polarity is
stimulating the nerve, the pulses have to be charge balanced so
that an equal amount of charge is drawn from the electrode as well
as pumped into the electrode. This is ensured by the last part of
the circuit. The transistor T1 is off as long as the transmitter is
active. When the transmitter turns off, the voltage on C1 decreases
which causes the base of T1 to be drawn low. While the pulse was
sent, C3 was charged. This charge is now sent back through T1 which
is on (D2 is blocking the other way) and backwards out through the
electrode. As it is not possible to have a net DC current running
through the capacitor (C3), a balanced stimulation is obtained
ensuring that electro-chemical processes are not formed, which can
destroy the tissue and the electrode. Zenerdiode Z1 is a protection
against too high a voltage in the circuit, which might be caused by
interfering magnetic fields in the relevant frequence area. When
the voltage is limited, a powerful lasting external field will not
be able to cause anything else but a single pulse on the electrode
with a charge of Qmax=VZ.times.C3=9,1V.times.470 nF =4,3 .mu.C
which in extreme cases can give a single powerful stimulation pulse
which, however, is not damaging to the nerve nor the electrodes.
The level of activation of the nerve/muscle is modulated by varying
the pulse duration. The width of the pulse is variable by means of
external transmitters e.g. between 0-255 .mu.s.
An external part of the stimulator, e.g. a corresponding telemetric
transmitter (not shown), is constructed by means of known
electrical elements.
In a preferred embodiment according to the invention, the
transmitter generates an electromagnetic burst of sine-waves of
approximately 5 MHz. The pulse is transmitted by two transmitting
coils (shown in FIG. 4) each made of six windings of copper wire
with a diameter of 0.375 mm, the coil diameter being approximately
90 mm. The coils can be positioned in such a way, that the
implanted stimulator is located in the homogeneous field created
between the two transmitting coils.
The coils can for example be located or incorporated in different
kinds of clothing, such as stockings, trousers or the like.
It should be noted that the electrical components wholly or partly
may be manufactures in an integrated circuit, such as ASIC-designs
or the like.
Moreover, it should be noted that the electrical environment of the
electrodes in many applications preferably may be digital, as a
coded multichannel remote signal is free of crosstalk between the
channels.
Referring now to FIG. 3, there is shown a stimulator according to
the invention, said stimulator comprising a receiver coil 33, which
is coupled to an electrical circuit 32. The electrical circuit 33
is furthermore connected to the dot electrodes 37, 38 and 39.
The stimulator further comprises a second receiver coil 43 which,
in this embodiment, is coupled to a second electrical circuit 42.
The second electrical circuit 43 is furthermore connected to the
dot electrodes 47, 48 and 49.
The stimulator is thus a two channel stimulator with two separately
operating receiving circuits, the circuits and the corresponding
electrodes 31 and 41 being individually addressable. The electrodes
are so-called dot-electrodes, which means that only a part of the
ring-shaped electrode means is a electrode contact area in this
embodiment. The stimulator is thus able to make a selective
stimulation of the nerve and the associated muscles, when implanted
around a nerve.
It is also possible within the scope of the invention to adapt the
stimulator with several receiving channels. In one embodiment
according to the invention the first receiving circuit is tuned to
approximately 3.5 MHz and the second receiving circuit is tuned to
approximately 4.7 MHz.
In FIG. 4 is shown how the stimulator 50 in FIG. 3 is mounted on
the nerves 51 leading to the muscles 52 in a limb 53. As it is
apparent from the drawing, two receiver coils 33 of the stimulator
are placed parallel with the skin. The transmitter coils 54 are
mounted in a bandage (not shown) placed around the limb. 55
designates the connection ends of the coils 54. The ends of the
bandage are equipped with velcro-closing for fastening the bandage
around the limb. The transmitter coils 54 are also lying flat on
the skin and is considerably larger than the receiving coils on the
stimulator. Due to the homogeneous electrical field and the size of
same, the location of the transmitter coils on the limb is less
significant.
The transmitter is operated by synchronous physiological signals
e.g. suitably arranged switches or sensors. In case of a dropfoot
patient by a heel switch or sensor.
According to the present invention the receiving coil and the
stimulating circuitry can be embedded in the wall of a nerve cuff
electrode. The transmitting coil consists preferably of two flat
coils, which are placed externally on each side of the implanted
stimulator. The device will work at shorter distances with only a
single transmitter coil.
The simple electronic circuitry combined with the use of very
small, but standard electronic components (surface mount
components), makes it possible to sufficiently reduce the size of
the circuit for it to be embedded in the wall of a nerve cuff.
Further the simple electronic circuitry makes it possible to avoid
the need for hermetic packaging, which is necessary if the circuit
contains naked silicon chips.
Integration of the stimulator into a nerve cuff makes the necessary
stimulation current very low. This means that the range of an
external transmitter can easily be made large enough for the
implant to be located deep within an extremity.
The receiving coils of the implanted stimulators lie parallel to
the skin when implanted on a nerve, which makes it possible to use
flat transmitting coils in the external transmitter. This is an
advantage compared to other micro stimulators where the
transmitting coil has to surround the implant. It means that the
transmitting coil can easily be mounted on fabric and strapped
onto/around the arm or leg with a velcro-closing or the like.
The use of two transmitting coils makes the range of the
transmitter larger and the field more homogeneous, thus making the
implanted stimulator less sensitive to movements with respect to
the external transmitter. Accordingly, it is not significant that
the transmitting coils are placed in the exact optimal position
which can be difficult for the users who are typically disabled
people who are paralysed in one side of their body
The lack of lead wires makes the device less susceptible to damage,
since malfunction of an implanted device is often caused by broken
wires. Also the risk of damage to the nerve in the chronic implant
is reduced, since nerve damage is often a result of the wires
pulling on the electrode. Also the lack of wires renders the device
more simple to install.
* * * * *